Our long term goal is to understand the nucleo/cytoplasmic interactions important for the biogenesis of mitochondria and our strategy has been to focus on the expression of mitochondrial tRNAs and the tRNA biosynthetic enzymes necessary to process the primary transcripts of mitochondrial tRNA genes. RNase P, the enzyme which removes the 5' leaders from tRNA precursors is a ribonucleoprotein enzyme consisting of both mitochondrial and nuclear gene products. Biochemical and genetic studies have shown the nuclear coded protein subunit, Rpm2p, is multifunctional and required for tRNA processing as well as processing of the mitochondrial RNA subunit of the enzyme, Rpm1r. Unexpectedly, deletion of RPM2 revealed it to have an essential function, unrelated to its role in the activity and biogenesis of mitochondrial RNase P. Four specific aims seek to discover what each function is, how a single gene provides each function, and whether, as a multifunctional protein, RPM2 could play a coordinating role in integrating mitochondrial biogenesis with the overall needs of the cell. In aim 1 we will use biochemical, genetic and molecular approaches to test the hypothesis that the role of Rpm2p in the maturation of Rpm1r is as a chaperone and/or "organizer" for the enzymes which process the 5' and 3' ends of Rpm1r. Aim 2 seeks rpm2 mutants with defects in tRNA processing but not Rpm1r processing and essential functions so that biochemical approaches can be used to test the hypothesis that eukaryotic RNase P proteins play a role in tRNA processing which their prokaryotic counterparts do not. Biochemical, molecular, cell biological and genetic approaches described in aims 3 and 4 address the essential function of Rpm2p and whether it may play a coordinating role in integrating mitochondrial biogenesis with the overall needs of the cell. Mitochondria play a central role in cellular metabolism and defects in mitochondrial biogenesis are known to be the underlying cause of an increasing number of inherited mitochondrial myopathies. Basic understanding of the nucleo-cytoplasmic interactions necessary for organelle biogenesis have, in the past, and will in the future, contribute insights to understanding and treating human disease.